The present invention relates to a unique coating process that involves the simultaneous extrusion and coating of polymeric tubes.
Medical devices for insertion into the body such as catheters and dilatation balloons attached to the distal end of such catheters, are formed from polymeric materials such as polyolefins including polypropylene and polyethylene, ethylene copolymers, polyvinyl chloride, polyurethane, polyesters, polyamides, polyether block amide elastomers, other thermoplastic elastomers, and so forth. These materials are typically inherently nonlubricious. It is desirable that these surfaces be lubricated for a variety of reasons including the reduction of catheter or wire movement frictions, the minimization of thrombosis, tissue trauma, tissue adhesion, pain, and so forth.
Coatings are commonly used in the medical device area for rendering such inherently non-lubricious substrate surfaces lubricious, as well as for protecting the surfaces of these devices, especially dilatation balloons. These coatings may be either hydrophilic or hydrophobic. Furthermore, because such medical devices are often inserted through the skin and into the body and are withdrawn at a later time, or as noted above, travel over long distances through small orifices, it is also necessary to have coatings which can be retained on the surface of the device for a long period, even when exposed to an aqueous environment, and is stable throughout the medical procedure.
Common hydrophobic coatings include fluoropolymers, siloxanes, mineral oil, sesame oil, glycerine, olive oil, polytetrafluoroethylene, and so forth. Hydrophobic coatings of an oily nature, have low surface energies and have a tendency to bead up and migrate over the surface of the device.
Another approach for reducing the coefficient of friction is to add a layer of a low friction material such as polytetrafluoroethylene, hereinafter PTFE and commonly known by the tradename of Teflon(copyright). The problem with the use of PTFE is that it typically requires a separate extrusion process, and also requires etching. Adhesion is also generally a problem between the PTFE and the polymeric materials from which medical devices are made.
Hydrophilic coatings, upon exposure to an aqueous environment, can also migrate from the surface of the device which decreases the efficacy of the lubricious coating, particularly when the coating is in a liquid or gelled state.
There have been a variety of approaches utilized in order to increase the retention time of coatings on the surface of the medical device. These methods include altering the surface of the device such as through high energy radiation, bonding the coating to the surface of the device by direct chemical bonding, in situ polymerization processes, or by forming interpolymer networks.
The radiation process suffers from inconsistency and unreliability in alteration of the polymeric surface, and can produce radiation damage to the substrate. Interpolymer networks can be disrupted and break with turbulent flow, or with extended periods of exposure to an aqueous environment, resulting in the hydrophilic portion washing away from the surface of the device. Chemical bonding and in situ polymerization often decreases process efficiency due to the fact that typically several steps are involved in such a process.
In U.S. Pat. No. 4,373,009 to Winn, a substrate surface is primed with solution of a polyisocyanate, followed by a solution of a hydrophilic copolymer. The hydrophilic copolymer is capable of chemically reacting with a coupling agent which will promote adhesion to the substrate.
U.S. Pat. No. 4,720,521 to Spielvogel describes a film-forming silicone composition having a non-reactive lubricating component which is a siloxane polymer dispersed or distributed within a reactive component which is a mixture of siloxane polymers, such that when the composition is applied to or used in conjunction with a substrate surface, it coats and adheres to the surface while providing surface lubrication.
U.S. Pat. No. 5,084,315 issued Jan. 28, 1992 to Karimi et al. describes a coating composition which has at least two and preferably three or more components. The first component is a hydrophilic lubricating polymer which provides lubricity to the coated article when wet. The second component is a polymeric matrix material which serves as a carrier for the lubricating polymer and as a binder to provide adherence of the coating composition to the base polymer. The nature of the matrix polymer depends on the base polymer and preferably includes a polyurethane. For instance, when the base polymer is PVC, the matrix material preferably is an alloy of PVC and the matrix polyurethane.
U.S. Pat. No. 5,266,359 issued Nov. 30, 1993 to Spielvogel describes a coating composition for an article which comprises an aqueous emulsion of a surfactant and a noncuring polysiloxane lubricant substituted by a polar group, referred to by Spielvogel as the polar lubricant. Spielvogel states that the lubricant used on a metal article, because of the polar group, is adsorbed into the metal and adheres to the surface significantly reducing the wipe-away that occurs when inserting the medical device into the skin. Spielvogel discloses that a plastic catheter tubing may also be coated with the polar lubricant, but preferably is coated with a nonpolar polysiloxane lubricant, and specifically mentioned is trialkylsiloxy terminated polysiloxane.
U.S. Pat. No. 5,919,570 to Hostettler et al. issued Jul. 6, 1999 describes tenaciously adhering coatings of commingled hydrogels composed of a polyurethane/urea polymer hydrogel in combination with at least one dissimilar hydrogel, i.e. poly(N-vinylpyrrolidone) polymer hydrogel, and a process for making such commingled hydrogels, especially where the substrate materials to which they are applied are polymeric materials which are intrinsically non-polar and hydrophobic. Hostettler et al. further describes a process whereby the surface of the hydrophobic polymers are treated in order to render them more polar and hydrophilic so that the tenaciously adhering, slippery commingled hydrogel coatings may subsequently be applied to the polymer surface.
U.S. Pat. No. 5,824,173 issued Oct. 28, 1998 to Fontirroche et al. describes a method of making an intravascular balloon catheter which includes forming an inner shaft by coextruding a flexible plastic tube by bringing a molten outer plastic layer into contact with a molten inner plastic layer, thereby bonding the plastic layers together during the coextrusion process. The inner plastic layer may be more lubricious than the outer plastic layer.
U.S. Pat. No. 5,061,424 issued Oct. 29, 1991 to Karimi et al. describes a method for coextruding a melt of a substrate polymer and a melt of a coating composition comprising polyvinylpyrrolidone and a base polyurethane which gives a shaped article of a substrate polymer with a layer of a coating composition that becomes lubricious when the substrate comes into contact with a liquid.
Surprisingly, the influence of the chemical and physical composition of body fluids, as well as the dynamic forces of the bodily fluids, has a drastic influence on the permanence or retention of the coatings used on medical devices. Hydrophilic polymers may be washed from the surface by bodily fluids and silicone coatings tend to bead and lose their efficacy in the presence of bodily fluids.
Accordingly, there remains a need in the art of medical devices for coatings that are both lubricious and increase the durability of the balloon which have superior retention or wear permanence on the surface of medical devices, especially those constructed from polymeric materials.
The present invention relates to a method of applying a lubricious and protective coating to a polymeric tube simultaneously with extrusion of the tube while the tube is at temperatures of greater than ambient. The tube may be coated on the inside and/or outside as it is being extruded. It is an object of the present invention to provide a one step process that combines the extrusion and coating processes of tubular members that may be used in medical devices. A thin coating is preferably provided on the inside of the tubular member. The coating method, in addition to providing efficiency in the manufacturing process, also provides improved adhesion, and retention, of a lubricious coating to a polymeric medical device.
Specifically, the present invention relates to a method of preparing a coated hollow polymeric tube by extrusion. The tube has an inner surface and an outer surface. The method involves forcing a stream of molten base polymer into an entry port at one end of an extruder shaping die, and applying a coating to the base polymer while it is in the shaping die of the extruder, and prior to the tube exiting the discharge port of the shaping die. The coating is therefore applied while the tube is in its molten form. The coating may be applied either to the inner surface of the tube, or to the outer surface of the tube.
This coating method simplifies the process while improving adhesion without surface priming or chemical bonding. Applying the coating to the polymeric tube during extrusion while the tube is above ambient temperature provides better adhesion of the coating to the tube.
These coated tubes may be used in medical devices such as catheter assemblies.